Most people do not know of the problems that exist in accurately measuring vitamin D levels. If they had their blood drawn five times on the same day, they may well get back five different 25(OH)D levels, and the differences could be significant.

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About John Cannell, MD

Dr. John Cannell is founder of the Vitamin D Council. He has written many peer-reviewed papers on vitamin D and speaks frequently across the United States on the subject. Dr. Cannell holds an M.D. and has served the medical field as a general practitioner, emergency physician, and psychiatrist.

Has anyone looked at the effect of supplementation timing in relation to test results? I have started having my patients hold their supplemental vitamin D the day of a blood draw, just in case the dose might falsely elevate their blood levels.

Progress in 25(OH)D testing has larger potential importance. It is hard to imagine anything that would cause interest in vitamin D to grow as dramatically as a 25(OH)D test as straightforward and cheap as the self blood test used by diabetics.